AC 20-74 29 July 1971 EXAMPLE OF TYPICAL EFFECTIVE INTENSITY • CALCULATION AREA IN SQ. IN. X SEC. PER IN, X CANDELAS PER IN.
BASED ON I MAX. -(t2 - $, IN INCHES X SECONDS PER IN.) + .2 IST ESTIMATE (O SEC. PER IN. = .0666 AREA BETWEEN LIMITS to and to = 9.0 SQ. IN.
DISTANCE FROM ta TO t20 - = 7.04 IN
9.00 × 0666 × 20 - = 17.9 CANDELAS
(7.04 X 0666) +.2 2ND ESTIMATE (b) SEC, PER IN. =.0666 DISTANCE FROM 6¡b'TO 12% AREA BETWEEN LIMITS tib and t2b = 4.60 SQ. IN. 2.165 N.
4.80 x .0666 × 20 - = 17.8 CANDELAS
(2.165 x.0666) +.2 3RD ESTIMATE (c) SEC. PER IN. = .0666 AREA BETWEEN LIMITS tye AND tc = 7.13 SQ. IN.
DISTANCE FROM. E€ TO C- _ = 4.765 IN
4.60 X 1. 0666 × 20 + = 18.4 CANDELAS
(4.765 × .0666) +.2
18.4 X 1,12 (HEAT CORRECTION FACTOR) = 20.6 CANDELAS - 80
THIS CURVE TAKEN AT -20° ELEVATION (c) CANDELAS
• 40
- 2.165"
4.765" , 7.040" FIGURE 3.8 Page 34 Chap 13
29 July 1971 AC 20-74
TYPICAL FLASHTUBE MEASUREMENT DATA SHEET Input Voltage - 14.0, Flash Capacitor 177 MFD.
Charge Voltage - 420 V., 15.6 Watt-Seconds Flash Rate - 1 per second.
Vertical Angle - 0° Test Distance - 5.0 ft.
BPI = Single flash reading × D2 x 5, (Multiplier = 125) Horizontal Distribution Data HOR. METER NO. OF FLASHES AVG. READING DEG. INTEGRATED FOR SINGLE FLASH EFI
19.8 10 1.98 248.0 10° 22.0 10 2.20 275.0 20° 30° 007 50° 009 70° 80° 90° 0O0T 110° 1200 130° 8.8 10 -88 110.0
TYPICAL FLASHTUBE MEASUREMENT Chap 3 Par 10 Page 35(and 36)
29 July 1971 AC 20-74 Appendix 1 APPENDIX 1
GLOSSARY OF TERMS
1. CANDELA - Unit of intensity. Produces one lumen per unit solid angle (steradian) . At a distance of one foot, one candela produces an illuminance of one footcandle.
2. CHROMATICITY - The color quality of light determined by its chromaticity coordinates.
3. COLORIMETRY - A method for measuring colors and specifying them in numerical or definite symbolic terms.
4 - COLOR TEMPERATURE - The temperature at which a blackbody must be operated to give the same color as the source, usually expressed in Kelvins (K).
S. DOMINANT WAVELENGTH - That wavelength of spectrum light which, when combined with neutral light in suitable proportions, matches the color. Neutral light is light for which the chronaticity
6. EXPOSURE - The product of the 1lluminance and the time during which the material is exposed to this illuminance, or E = it. The unit of measure is the footcandle-second, which represents an exposure of 1 second to a source having a light intensity of 1 candela at a distance of 1 foot.
7. HUE - The attribute of color determined primarily by the wavelength of light entering the eye.
8. ILLUMINANCE - The areal density of luminous flux incident on a surface, in lumens per unit area or footcandles.
9. INTENSITY - Flux per unit solid angle from a point source measured in lumens per steradian or in candelas; often called candlepower.
10. LIGHT - Radiant energy that produces visual sensations.
11. LUMEN - Unit of luminous (visible) flux. Luminous energy emitted per second by a uniform point source of one candela intensity through a solid angle of one steradian.
12. LUMINANCE - Luminous intensity of a surface in a given direction per unit of projected area of the surface as viewed from that direction;
measured in candelas per unit area.
Page 1 Par 1
AC 20-74 29 July 1971 Appendix 1
13. LUMINOUS FLUX - The time rate of flow of light, sometimes called light power.
14. PHOTOMETER- An optical device that utilizes equations of brightness or flux to permit the measurement of a photometric quantity, such as intensity, illuminance or brightness.
PHOTOMETRY - The measurement of visible radiation on the basis of its effect upon the eye under standard conditions. Visual photometry involves the adjustment of two parts of the visual field, in order to identify or to determine a minimal difference. Photoelectric photometry involves the measurement of the flux incident on a receiver fron a test and a standard source at known distances.
16. SATURATION - The extent to which a chromatic color differs from grey of the same brightness, measured on an arbitrary scale from 0% to 100% (where grey 18 0%). Also called "purity".
17. SPECTROPHOTOMETER - An instrument designed to measure the spectral transmittance or reflectance of objects. Used primarily for comparing, at each wavelength, the flux leaving the object with the flux incident upon it. It usually has a built-in light source.
18. SPECTRORADIOMETER - An instrument used to measure the spectral distribution of radiant energy.
SPECTRAL LUMINOUS EFFICIENCY V(1) - Quotient of the luminous flux at a given wavelength by the radiant flux at that wavelength normalized by dividing by the maximum value of that quotient, formally called
20. STERADIAN - The unit solid angle. That solid angle originating at the center of a sphere which subtends an area on the surface of that sphere equal to the square of its sphere radius. A sphere containa 47 steradians (see Figure 1.3).
Page 2 Par 13
PHOTOMETRIC TERAS 29 July 1971
QUANTITY SYMBOL DESCRIPTION UNIT EQLIVALENT CONVERSIONS Flux Rate of Flow of Light lumen lumens • watc: x 680 x V(9) Intensity Point Source Light Power cande la 1 lumen/steradian candelas = foutcandles x distance squared (1/7) candelas/it- Luminance Concentration of Intensity crom Suriace Source footlambert V/452 candélas/in- (brightness) lambert 1 lumen/cm2 2.054 candelas: 1n2 Illuminance E Surface Received Light foctcandle 1 lumen'it- footcandles - candelasdistance Density squared Wavelength Distance a Cycle Traveled During meter Ratio frequency of of velocity to radiation meter - 1010 106 micrometers (nu) 109 nanometers (nm) angstroms (A°) Solid Angle Two Dimension Angles steradian Total Solid Angles/47 steradians • surface area! distance square:
(Sphere) Electrical Energy Rate watt Joules / Sec Power Eye Response to Varying uminou fficienc Wavelengths (Table 1.1) Page 1(and 2) Append 1x ~ AC 20-74
29 July 1971 AC 20-74 Appendix 3 APPENDIX 3
TRISTIMULUS COLORIMETRY AND AVIATION LIGHTS Although the energy distribution of a colored light may extend throught the visible spectrum, the characteristics of vision are such that a combination of three primary colors can match the light to the satisiaction This method of matching or reproducing a color is the basis for tristimulus colorimetry. The tristimulus method is to measure the energy distribution and then to convert this information int»› the tristimulus values which form a metameric match. Figure 1.4 of this circular shows how to mix the three CIE primary colors in order to match any wavelength. If we have energy distribution throughout the visible spertrum, we simply multiply the relative power amplitude at cach wavelength by the rorresponding tristimulus values x, y, and z for that wavelength. Thu, by adding up all the measurements a total amount for each of the primaries is found. Mixing these amounts of X (red), Y (green), and Z (blue), we accomplished a metameric match. Thus.
X = 1380 EX A where F is the power, and & is the proportion of red primary required for that wavelength; Y and Z are found similarly.
In this way, we can determine the required amounts of primaries to match the color of a source or in the case of lights, the lamp. C.I.E. standard illuminant "A" (incandescent) has a published power distribution, as have several other sources, and tables of Ex, Ey, and Ez are available. If the source is non-standard, the E values must be measured, and by computation, the tables developed. The significance of this information is that the color of the light transmitted by the filter depends not only on the filter but also on the spectral distribution of the light incident on it.
After tabled values for Ex, etc., are developed, they must be modified by the filter effect. Usually, this is done by measuring the filters' transmittances throughout the visible spectrum. This gives a new column labeled 'r". Then, to obtain the X, Y, and 2 required to form a match of the overall system, we must combine the data. Combining the source and filter data we solve the equations:
X = [380 Ex TA) etc.
Mechanically this is done as follows:
1. Measure the power distribution of the light source (E) in 10 nanometer steps from 380 to 770 nanometers (40 measurements).
.AC 20-74 29 July 1971 Appendix 3
2. For each step, combine (by multiplication) x, y, and z information from tabled values to obtain Ex, Ey, and Ez (40 values).
3. Measure the transmittance (r) of the filter at these same 40 points. Combine these numbers with previously computed values to obtain 40 values tor EXT, Eỹi, Ežt.
4. Add the 40 values for Ext to obtain X; the amount of red primary required for a match. Repeat for Eyt and EZt to obtain Y and Z.
5. Compute x = X+Y+Z x+ + 2 and 2* x++2 • This gives the chromaticity coordinatos which will form a metameric match of the light color.
The transmittance of a light filter is,by definition, the ratio of transmitted to incident light power. The transmittances (r) measured at the 40 sample points do not consider eye response, nor the power distribution of the 1lluminant. Therefore, when we evaluate a filter for overall transmittance, we must combine the following data:
1. Power distribution of. source . • •E
2. Eye response luminous-efficiency function . • y [ý was adjusted to correspond to V(1)]
3. filter transmittance distribution . . • • T These three variables were combined when developing Y as I??0 Ey T41. As this is also a measurement of visible transmitted light magnitude, dividing by the incident light will give the transmittance of the filter. The talent ances marafare as the rent lied 15536 we alt the filter transmittances. Therefore, and the transmittance I = I380 Ey T41 .
- 770 Page 2.
: C 211-74 29 July 1971 Appendix 4 APPENDIX 4
BIBLIOGRAPHY
1. vision in MilItary Aviation - WADC Terhnical Report 58-399, ASTIA Document No. AU 207780.
2. Fundamentals of Light and Lighting veneral Flectric Company, Large Lamp Department, Cleveland, Ohfu.
3. Pederal Standard No. J, with Amendwent 1, March 21, 1951. Superintendent ot Documents, Washington, D. C. 20402.
+. Mi1-C-25050A(ASG) December 2, 1763 - Colors, Aeronautical Lights and Lighting Equipment, General Requirements For.
5. Color and Transmission Properties of Sharp Cut-Off Glass Filters it Elevated Temperatures - C. E. Leberknight and G. E. Stone, Kopp Glass, Inc., Swissvale, Pennaylvania, April 1955.
6. Specification for Photometric Test Procedure, Specification CAA-110., June 10, 1957, Department of Commerce, Civil Aeronautics Administration, Office of the Air Navigation Facilities, Plant Engineering Division, Washington, D. C. 20402.
7. A Short Course in Photometry, Leu Levi, Consulting Physicist, New Yo:k.
New York, Electronics Products, February 1965.
8. Collision Avoidance and Aircraft Lighting, Grimes Manufacturing Co., Urbana, Ohio, 1965.
9. Measurement of the Effective Candlepower of Flashing Beacons - Charles A. Steinberger and Marshal F. Rowland, Grimes Manufacturing Co., Urbana, Ohio, 1965.
10. Illuminating Eugineering Society Lighting Handbook, Fourth Edition.
1l. Illuminating Engineering Society Guide for Calculating the Effective Intensity of Flashing Lights, Illumination Engineering, 59 747 (1964).
12. Photometry of Colored Lights - A. C. Wall, Illuminating Engineering, 1967.
13. MIL-L-25467C Lighting, Integral, Aircraft Instrument, General Specification For, (Dec. 1963).
14. Colors of Signal Lights, NSS Monograph 75, (1967). Superintendent of Documents, Washington, D. C. 20402.
15. U. S. Standard for Colors of Signal Lights, (1964).
AC 20-74 29 July 1971 Appendix 4
16. 1968 NEREM Technical Publications. How to Measure Light - P.B. Lape and D. V. Ryer, International Light, Inc., Newburyport, Maas.
17. Illumination Engineering - Warren B. Boast, 1953.
18. Colorimetry, NBS Monograph 104, 1968. Superintendent of Documents, Washington, D. C. 20402.
19. Light and Color Measurements of Small Light Sources, Boris Meric, General Electric Small Lamp Diviaion, Nela Park, New York.
20. The Measurement of the Color of Light Emitted by Signal Devices, by Stewart Sease and Paul M. Fisher, Rohm and Haas Color Laboratory, Available as a reprint from "Color Engineering," Reprint Dept., 18 John Street, New York, New York 10038.
21. The Application of a Color-Correction Factor in the Photometry of Colored Signal Lights by George K. C. Hardesty and I. O. Iwiat, Neval Ship Research and Development Laboratory, Annapolis, Maryland (Technical Note ELECLAB 125/68 of May 1968)
22. Maximum Luminous Efficiency Contour Charts for Colored Materials by George K. C. Hardesty, R. L. Booker, and J. I. Mclane, Naval Ship Research and Development Laboratory, Annapolis, Maryland 21402 (Technical Note, ELECLAB 200/68 of October 1968).
23. Photometry, W. I. Welsh Constable, Third Edition, 1958.
24. The Role of Exterior Lights in Mid-Air Collieion Prevention, T.H.
Projector, Applied Paychology Corp., July 1962, ASTIA Document AD 602421.
25. Computation of the Effective Intensity of Flashing Lights, C. A. Douglas, Illumination Engineering, Vol. 52, page 641, December 1957.